2025年4月3日星期四

Urban heat island

Urban areas usually experience the urban heat island (UHI) effect, that is, they are significantly warmer than surrounding rural areas. The temperature difference is usually larger at night than during the day, and is most apparent when winds are weak, under block conditions, noticeably during the summer and winter. The main cause of the UHI effect is from the modification of land surfaces, while waste heat generated by energy usage is a secondary contributor. Urban areas occupy about 0.5% of the Earth's land surface but host more than half of the world's population. As a population center grows, it tends to expand its area and increase its average temperature. The term heat island is also used; the term can be used to refer to any area that is relatively hotter than the surrounding, but generally refers to human-disturbed areas.

Monthly rainfall is greater downwind of cities, partially due to the UHI. Increases in heat within urban centers increases the length of growing seasons and decreases the occurrence of weak tornadoes. The UHI decreases air quality by increasing the production of pollutants such as ozone, and decreases water quality as warmer waters flow into area streams and put stress on their ecosystems.

Not all cities have a distinct urban heat island, and the heat island characteristics depend strongly on the background climate of the area in which the city is located. The impact in a city can change a lot based on its local environment. Heat can be reduced by tree cover and green space which act as sources of shade and promote evaporative cooling. Other options include green roofs, passive daytime radiative cooling applications, and the use of lighter-colored surfaces and less absorptive building materials. These reflect more sunlight and absorb less heat.

Climate change is not the cause of urban heat islands but it is causing more frequent and more intense heat waves which in turn amplify the urban heat island effect in cities (see climate change and cities).  Compact, dense urban development may increase the urban heat island effect, leading to higher temperatures and increased exposure.

Definition
A definition of urban heat island is: "The relative warmth of a city compared with surrounding rural areas."  This relative warmth is caused by "heat trapping due to land use, the configuration and design of the built environment, including street layout and building size, the heat-absorbing properties of urban building materials, reduced ventilation, reduced greenery and water features, and domestic and industrial heat emissions generated directly from human activities". 

Description
An urban heat island (abbreviated UHI) is a localized elevation of temperatures, particularly daytime and nighttime maximum temperatures, recorded in an urban environment relative to neighboring rural or forested areas or relative to regional average temperatures. This heat dome creating a kind of urban microclimate (en) would be understood and described for the first time in 19th century London by Luke Howard, a pharmacist with a passion for meteorology who published in 1818-1820 The Climate of London in two volumes, in which he noted a difference in daytime temperatures of 0.19 °C and nighttime temperatures of around 3.7 °C between central London and its countryside. Cities are warming faster than the rest of the country. Modelling and interactive maps produced by the European Environment Agency show which European cities are most affected by climate change, based on data collected from around 500 cities.

The island is favored by different uses and land covers (mineralization of public space, city configurations which reduce cooling by winds and evapotranspiration, density of buildings which absorb heat and release it slowly during the night in the form of infrared radiation), as well as by anthropogenic sources of heat emission (hot air emissions linked to road traffic, public lighting, industries, heating and air conditioning, etc.). Within the same city, significant differences in temperature can be noted depending on the nature of the land use (forest, bodies of water, suburbs, dense city, etc.), the albedo, the relief and the exposure (south or north slope), and of course depending on the season and the type of weather.

Heat islands are artificial microclimates that can have significant impacts by creating situations of thermal discomfort that have a detrimental effect on human health (respiratory failure, cardiovascular, cerebrovascular, neurological and renal diseases) and on urban energy consumption.

This warming seems to be worsening, and requires new adaptation strategies (HIC reduction strategies: limitation of mineralized surfaces, greening of buildings and urban spaces, water retention by the ground or in basins, eco-construction and transport management reducing the production of anthropogenic heat, increase in surface albedo),.

Diurnal variability
Throughout the daytime, particularly when the skies are cloudless, urban surfaces are warmed by the absorption of solar radiation. Surfaces in the urban areas tend to warm faster than those of the surrounding rural areas. By virtue of their high heat capacities, urban surfaces act as a reservoir of heat energy. For example, concrete can hold roughly 2,000 times as much heat as an equivalent volume of air. As a result, high daytime surface temperatures within the UHI can be easily seen via thermal remote sensing. As is often the case with daytime heating, this warming also has the effect of generating convective winds within the urban boundary layer. At night, the situation reverses. The absence of solar heating leads to the decrease of atmospheric convection and the stabilization of urban boundary layer. If enough stabilization occurs, an inversion layer is formed. This traps urban air near the surface, keeping surface air warm from the still-warm urban surfaces, resulting in warmer nighttime air temperatures within the UHI.

Generally speaking, the difference in temperature between the urban and surrounding rural area is more pronounced at night than in daytime. For example, in the United States, the temperature in urban areas tends to be warmer than the surrounding area by about 1–7 °F (−17 – −14 °C) during the daytime, and about 2–5 °F (−17 – −15 °C) warmer at night. However, the difference is more pronounced during the day in arid climates such as those in southeastern China and Taiwan. Studies have shown that diurnal variability is impacted by several factors including local climate and weather, seasonality, humidity, vegetation, surfaces, and materials in the built environment.

Seasonal variability
Seasonal variability is less well understood than diurnal variability of the urban heat island temperature difference. Complex relationships between precipitation, vegetation, solar radiation, and surface materials in various local climate zones play interlocking roles that influence seasonal patterns of temperature variation in a particular urban heat island.

Measurements and predictions

Urban Heat Island Index (UHII)
One method to quantify the UHI effect within urban areas is the UHI Index created by the Californian EPA in 2015. It compares the temperature of a surveyed area and rural reference points upwind from the surveyed area, at a height of two meters above ground level. The difference in temperature in degrees Celsius is taken hourly and differences with an increased urban temperature compared to the reference points are summed up, creating an amount of degree-Celsius-hours, which is the UHI Index of the surveyed area. The measure of Celsius-hours might be averaged over many days, but is specified as Celsius-hours per averaged day.

The index was created to estimate the expected use of air conditioning and resulting greenhouse gas emissions in California. The index does not consider values of or differences in wind-speed, humidity, or solar influx, which might influence perceived temperature or the operation of air conditioners.

Models and simulations
If a city or town has a good system of taking weather observations the UHI can be measured directly. An alternative is to use a complex simulation of the location to calculate the UHI, or to use an approximate empirical method. Such models allow the UHI to be included in estimates of future temperatures rises within cities due to climate change.

Leonard O. Myrup published the first comprehensive numerical treatment to predict the effects of the urban heat island (UHI) in 1969. The heat island effect was found to be the net result of several competing physical processes. In general, reduced evaporation in the city center and the thermal properties of the city building and paving materials are the dominant parameters. Modern simulation environments include ENVI-met, which simulates all interactions between building and ground surfaces, plants and ambient air.

Causes
These “heat bubbles” are induced by the intersection of two factors:
more intense human activities, especially concentrated in cities. Some of these activities are significant and chronic sources of heat, such as factories, internal combustion engines, aircraft jet engines (especially during takeoff), boilers (individual or collective), air conditioning systems, hot water circulating in sewers, old and sometimes poorly insulated heat networks, etc.;
a change in the nature of the ground surface, with urbanization making the city more absorbent of solar radiation than a natural or cultivated environment. Black surfaces (tar, tarred terraces, dark materials, and many glass buildings) behave like solar collectors or greenhouses which then return this energy in the form of infrared radiation, which heats the urban air and, in the absence of wind, the entire urban environment. The city has the effect on wind patterns of reducing their speed because of the many obstacles it creates, which reduces the cooling action of the winds which dissipate the accumulation of heat, evacuate overheating, and promote evapotranspiration.

The greatest accumulation of heat is determined by a series of interacting causes, among which we must mention the widespread concreting, the asphalt surfaces that clearly prevail over the green areas, the emissions from motor vehicles, industrial plants and heating and air conditioning systems for domestic use. At the same time, the perimeter walls of city buildings prevent the wind from blowing with the same intensity that is recorded in open areas outside the city: the wind effects can be up to 30% lower than in neighboring rural areas, thus limiting the recirculation of air at the ground and the related cooling effect during the summer season. In urban areas, moreover, the ratio between horizontal surfaces and vertical surfaces is lower, which inhibits the dispersion of heat through thermal radiation.

Generally, the heat island effect is directly proportional to the extension of the urban area, so much so that it can create conditions that lead to detecting temperatures that are on average between 0.5 and 3 °C higher than in the surrounding countryside. The increase in temperatures concerns both winter minimums and summer maximums; while in the first case the consequence is a smaller number of days of frost and/or ice, in the second case it can determine a greater intensity of heat waves.

Urban design
There are several causes of an urban heat island (UHI) related to common urban design aspects. For example, dark surfaces absorb significantly more solar radiation, which causes urban concentrations of roads and buildings to heat more than suburban and rural areas during the day; materials commonly used in urban areas for pavement and roofs, such as concrete and asphalt, have significantly different thermal bulk properties (including heat capacity and thermal conductivity) and surface radiative properties (albedo and emissivity) than the surrounding rural areas. This causes a change in the energy budget of the urban area, often leading to higher temperatures than surrounding rural areas.

Pavements, parking lots, roads or, more generally speaking transport infrastructure, contribute significantly to the urban heat island effect. For example, pavement infrastructure is a main contributor to urban heat during summer afternoons in Phoenix, United States.

Another major reason is the lack of evapotranspiration (for example, through lack of vegetation) in urban areas. The U.S. Forest Service found in 2018 that cities in the United States are losing 36 million trees each year. With a decreased amount of vegetation, cities also lose the shade and evaporative cooling effect of trees.

Other causes of a UHI are due to geometric effects. The tall buildings within many urban areas provide multiple surfaces for the reflection and absorption of sunlight, increasing the efficiency with which urban areas are heated. This is called the "urban canyon effect". Another effect of buildings is the blocking of wind, which also inhibits cooling by convection and prevents pollutants from dissipating. Waste heat from automobiles, air conditioning, industry, and other sources also contributes to the UHI.

Heat islands can be affected by proximity to different types of land cover, so that proximity to barren land causes urban land to become hotter and proximity to vegetation makes it cooler.

Air pollution
High levels of air pollution in urban areas can also increase the UHI, as many forms of pollution change the radiative properties of the atmosphere. UHI not only raises urban temperatures but also increases ozone concentrations because ozone is a greenhouse gas whose formation will accelerate with the increase of temperature.

Climate change as an amplifier
Climate change is not a cause but an amplifier of the urban heat island effect. The IPCC Sixth Assessment Report from 2022 summarized the available research accordingly: "Climate change increases heat stress risks in cities and amplifies the urban heat island across Asian cities at 1.5 °C and 2 °C warming levels, both substantially larger than under present climates."

The report goes on to say: "In a warming world, increasing air temperature makes the urban heat island effect in cities worse. One key risk is heatwaves in cities that are likely to affect half of the future global urban population, with negative impacts on human health and economic productivity." 

There are unhelpful interactions between heat and built infrastructure: These interactions increase the risk of heat stress for people living in cities. 

Impacts
These islands significantly reduce the effects of the cold in the city, but pose several problems.
At local levels (interior courtyards in particular) electric air conditioning can exacerbate the phenomenon; air conditioners cool the interior of the building, but by rejecting the calories into places that are sometimes poorly ventilated, which they heat up, which maintains overheating of the building.
They reduce urban dew, mists and fog (except in coastal towns and deep valleys). While dew and mists contribute to the problems of acid attack on buildings in areas where the air is acidic, they also help to purify the air of aerosols and certain suspended dust and pollen.
They increase air pollution by worsening smog and atmospheric inversion effects (sources of pollution confinement under the urban ceiling). They worsen the health effects.
They can contribute to modifying the physicochemical composition of the air, promoting certain photochemical pollution.
They reinforce the health and socio-economic effects of heat waves.
They disrupt the recording of regional and local temperature averages and therefore weather forecasts, because many weather stations were surrounded during the 20th century by an increasingly dense and "hot" urban fabric.
Precipitation increases over cities. As the air is slightly warmer over urban areas, cumulonimbus clouds will develop primarily in these regions and therefore thunderstorms will form primarily over cities.

On weather and climate
Aside from the effect on temperature, UHIs can produce secondary effects on local meteorology, including the altering of local wind patterns, the development of clouds and fog, the humidity, and the rates of precipitation. The extra heat provided by the UHI leads to greater upward motion, which can induce additional shower and thunderstorm activity. In addition, the UHI creates during the day a local low pressure area where relatively moist air from its rural surroundings converges, possibly leading to more favorable conditions for cloud formation. Rainfall rates downwind of cities are increased between 48% and 116%. Partly as a result of this warming, monthly rainfall is about 28% greater between 20 and 40 miles (32 and 64 km) downwind of cities, compared with upwind. Some cities show a total precipitation increase of 51%.

One study concluded that cities change the climate in area two–four times larger than their own area. One 1999 comparison between urban and rural areas proposed that urban heat island effects have little influence on global mean temperature trends. Others suggested that urban heat islands affect global climate by impacting the jet stream.

On human health
UHIs have the potential to directly influence the health and welfare of urban residents. As UHIs are characterized by increased temperature, they can potentially increase the magnitude and duration of heat waves within cities. The number of individuals exposed to extreme temperatures is increased by the UHI-induced warming. The nighttime effect of UHIs can be particularly harmful during a heat wave, as it deprives urban residents of the cool relief found in rural areas during the night.

Increased temperatures have been reported to cause heat illnesses, such as heat stroke, heat exhaustion, heat syncope, and heat cramps.

Extreme heat is the deadliest form of weather in the U.S. Per a study by Professor Terri Adams-Fuller, heat waves kill more people in the U.S. than hurricanes, floods, and tornadoes combined. These heat illnesses are more common within medium-to-large metro areas than the rest of the U.S., largely in part due to UHIs. Heat illnesses can also be compounded when combined with air pollution which is common in many urban areas.

Heat exposure can have adverse effects on mental health. Increases in temperature can contribute to increased aggression, as well as more cases of domestic violence and substance abuse. Greater heat can also negatively impact school performance and education. According to a study by Hyunkuk Cho of Yeungnam University, an increased number of days with extreme heat each year correlates to a decrease in student test scores.

High UHI intensity correlates with increased concentrations of air pollutants that gathered at night, which can affect the next day's air quality. These pollutants include volatile organic compounds, carbon monoxide, nitrogen oxides, and particulate matter. The production of these pollutants combined with the higher temperatures in UHIs can quicken the production of ozone. Ozone at surface level is considered to be a harmful pollutant. Studies suggest that increased temperatures in UHIs can increase polluted days but also note that other factors (e.g. air pressure, cloud cover, wind speed) can also have an effect on pollution.

Studies from Hong Kong have found that areas of the city with poorer outdoor urban air ventilation tended to have stronger urban heat island effects and had significantly higher all-cause mortality compared to areas with better ventilation. Another study employing advanced statistical methods in Babol city, Iran, revealed a significant increase in Surface Urban Heat Island Intensity (SUHII) from 1985 to 2017, influenced by both geographic direction and time. This research, enhancing the understanding of SUHII's spatial and temporal variations, emphasizes the need for precise urban planning to mitigate the health impacts of urban heat islands. Surface UHI's are more prominent during the day and are measured using the land surface temperature and remote sensing.

On water bodies and aquatic organisms
UHIs also impair water quality. Hot pavement and rooftop surfaces transfer their excess heat to stormwater, which then drains into storm sewers and raises water temperatures as it is released into streams, rivers, ponds, and lakes. Additionally, increased urban water body temperatures lead to a decrease in biodiversity in the water. For example, in August 2001, rains over Cedar Rapids, Iowa led to a 10.5 °C (18.9 °F) rise in the nearby stream within one hour, resulting in a fish kill which affected an estimated 188 fish. Since the temperature of the rain was comparatively cool, the deaths could be attributed to the hot pavement of the city. Similar events have been documented across the American Midwest, as well as Oregon and California. Rapid temperature changes can be stressful to aquatic ecosystems.

With the temperature of the nearby buildings sometimes reaching a difference of over 50 °F (28 °C) from the near-surface air temperature, precipitation warms rapidly, and run-off into nearby streams, lakes and rivers (or other bodies of water) to provide excessive thermal pollution. The increase in thermal pollution has the potential to increase water temperature by 20 to 30 °F (11 to 17 °C). This increase causes the fish species inhabiting the body of water to undergo thermal stress and shock due to the rapid change in temperature of their habitat.

Permeable pavements may reduce these effects by percolating water through the pavement into subsurface storage areas where it can be dissipated through absorption and evaporation.

On animals
Species that are good at colonizing can use conditions provided by urban heat islands to thrive in regions outside of their normal range. Examples of this include the grey-headed flying fox (Pteropus poliocephalus) and the common house gecko (Hemidactylus frenatus). Grey-headed flying foxes, found in Melbourne, Australia, colonized urban habitats following the increase in temperatures there. Increased temperatures, causing warmer winter conditions, made the city more similar in climate to the more northerly wildland habitat of the species.

With temperate climates, urban heat islands will extend the growing season, therefore altering breeding strategies of inhabiting species. This can be best observed in the effects that urban heat islands have on water temperature.

Urban heat islands caused by cities have altered the natural selection process. Selective pressures like temporal variation in food, predation and water are relaxed causing a new set of selective forces to roll out. For example, within urban habitats, insects are more abundant than in rural areas. Insects are ectotherms. This means that they depend on the temperature of the environment to control their body temperature, making the warmer climates of the city perfect for their ability to thrive. A study done in Raleigh, North Carolina conducted on Parthenolecanium quercifex (oak scales), showed that this particular species preferred warmer climates and were therefore found in higher abundance in urban habitats than on oak trees in rural habitats. Over time spent living in urban habitats, they have adapted to thrive in warmer climates than in cooler ones.

On energy usage for cooling
Another consequence of urban heat islands is the increased energy required for air conditioning and refrigeration in cities that are in comparatively hot climates. The heat island effect costs Los Angeles about US$ 100 million per year in energy (in the year 2000). Through the implementation of heat island reduction strategies, significant annual net energy savings have been calculated for northern locations such as Chicago, Salt Lake City, and Toronto.

Every year in the U.S. 15% of energy goes towards the air conditioning of buildings in these urban heat islands. It was reported in 1998 that "the air conditioning demand has risen 10% within the last 40 years."

Increases in air conditioning use also serve to worsen the effects of UHIs at night. While cooler nights are often a reprieve from heat waves during the day, the residual heat created by the use of air conditioning systems can lead to higher nighttime temperatures. According to a study by Professor Francisco Salamanca Palou and colleagues, this residual heat can cause nighttime increases of up to 1 °C in urban areas. Increased energy use from air conditioners also contributes to carbon emissions, which doubly exacerbates the effects of UHIs.

Options for reducing heat island effects
Strategies to improve urban resilience by reducing excessive heat in cities include: Planting trees in cities, cool roofs (painted white or with reflective coating) and light-coloured concrete, green infrastructure (including green roofs), passive daytime radiative cooling.

The temperature difference between urban areas and the surrounding suburban or rural areas can be as much as 5 °C (9.0 °F). Nearly 40 percent of that increase is due to the prevalence of dark roofs, with the remainder coming from dark-coloured pavement and the declining presence of vegetation. The heat island effect can be counteracted slightly by using white or reflective materials to build houses, roofs, pavements, and roads, thus increasing the overall albedo of the city.

Concentric expansion of cities is unfavourable in terms of the urban heat island phenomenon. It is recommended to plan the development of cities in strips, consistent with the hydrographic network, taking into account green areas with various plant species. In this way, it was planned to build urban settlements stretching over large areas, e.g. Kielce, Szczecin and Gdynia in Poland, Copenhagen in Denmark and Hamburg, Berlin and Kiel in Germany.

Urban planning as cause and solution
The structure and albedo of cities, as well as their lack of vegetation (which, moreover, when it exists, often differs greatly from natural flora and rural areas) predispose cities to heat bubbles. Environments with almost comparable mineral substrate rates (rocky cliffs) or plant substrates exist in nature (cliffs, canyons, etc.), but certain materials (glass, metal) and especially infrastructure such as waterproofed roads are not present there. The acceleration and strong artificialization of the water cycle are urban characteristics that have significant climatic impacts.

A first key factor is albedo, that is to say the measure of the capacity of a surface to reflect incident solar energy (which arrives at the surface of the Earth). It is a number between 0 and 1, 0 corresponding to a perfectly black body surface which absorbs all the incident energy, and 1 to the perfect mirror which reflects all the incident energy. Dark surfaces in fact absorb a significant quantity of solar energy and therefore heat up very quickly. Cities, mostly concreted and tarred, have dark surfaces which heat up very quickly in the sun, and which absorb during the day 15 to 30% more energy than an urban area. Sunny afternoons therefore allow the thermometer to display maximums much higher than the surrounding rural areas. The effect disappears at nightfall, which explains why maximum temperatures are generally the most affected. At night, materials that have accumulated daytime heat release some of it (slow restitution of heat by infrared radiation), limiting their ability to cool down where there is little air circulation ;

A second factor is the potential for evapotranspiration. Vegetation plays a very important role as a thermal regulator, partly through shade, but mainly through evapotranspiration, which cools the air, and dew, which has a thermohygrometric "buffer" effect. But the low rate of urban vegetation, particularly trees, limits this potential. The lawn has an albedo varying from 0.25 to 0.30 (slightly lower than the average terrestrial albedo, which is around 0.3). However, partial greening of the city can be optimized by sending runoff water to the plantations, a concept known as a rain garden or bioretention. The department of Seine-Saint-Denis and the City of Paris have calculated that a 100 m2 rain garden, which receives runoff water from an impermeable surface of at least 500 m2, can reduce the average temperature by one degree over a radius of one hundred meters. Thus, the installation of more than 400 m2 of rain gardens per hectare (i.e. a density of more than 4%) would make it possible, during a heatwave, to maintain an average temperature similar to that of a rural environment.

Urban planners rely on regional and local models of urban microclimates. Three-dimensional models take better account of sunlight, solar reflection and shadows, the nature and albedo of materials, and air circulation. They therefore theoretically allow for better positioning and prioritization of external insulation needs and alternative eco-technology (developments such as " green walls " or " green terraces " or plant screens of deciduous trees in summer, but which let the sun through in winter) in order to bio-climatize the city.

Planting trees in cities
Planting trees around the city can be another way of increasing albedo and decreasing the urban heat island effect. It is recommended to plant deciduous trees because they can provide many benefits such as more shade in the summer and not blocking warmth in winter. Trees are a necessary feature in combating most of the urban heat island effect because they reduce air temperatures by 10 °F (5.6 °C), and surface temperatures by up to 20–45 °F (11–25 °C). Another benefit of having trees in a city is that trees also help fight global warming by absorbing CO2 from the atmosphere.

Cool roofs and light-coloured concrete
Painting rooftops white has become a common strategy to reduce the heat island effect. In cities, there are many dark coloured surfaces that absorb the heat of the sun in turn lowering the albedo of the city. White rooftops allow high solar reflectance and high solar emittance, increasing the albedo of the city or area the effect is occurring.

Additionally, covering rooftops with a reflective coating, has shown to be an effective measure to reduce solar heat gain. A study led by Oscar Brousse from University College London, which simulated the impact of various cooling measures in London found that rooftops, which were either painted white or had reflective coating, proved to be the most effective solution for reducing outdoor temperatures at the pedestrian level, outperforming solar panels, green roofs, and tree cover. The study simulated the impact of various cooling measures in London during a 2018 heatwave, finding that the so-called cool roofs could reduce average outdoor temperatures by 1.2 °C, and up to 2 °C in certain areas. In comparison, additional tree cover reduced temperatures by 0.3 °C and solar panels by 0.5 °C.

Relative to remedying the other sources of the problem, replacing dark roofing requires the least amount of investment for the most immediate return. A cool roof made from a reflective material such as vinyl reflects at least 75 percent of the sun's rays, and emit at least 70 percent of the solar radiation absorbed by the building envelope. Asphalt built-up roofs (BUR), by comparison, reflect 6 percent to 26 percent of solar radiation.

Using light-coloured concrete has proven effective in reflecting up to 50% more light than asphalt and reducing ambient temperature. A low albedo value, characteristic of black asphalt, absorbs a large percentage of solar heat creating warmer near-surface temperatures. Paving with light-coloured concrete, in addition to replacing asphalt with light-coloured concrete, communities may be able to lower average temperatures. However, research into the interaction between reflective pavements and buildings has found that, unless the nearby buildings are fitted with reflective glass, solar radiation reflected off light-coloured pavements can increase building temperatures, increasing air conditioning demands.

There are specific paint formulations for daytime radiative cooling that reflect up to 98.1% of sunlight.

Green infrastructure
Green roofs are excellent insulators during the warm weather months and the plants cool the surrounding environment. Plants can improve air quality as they absorb carbon dioxide and concomitantly produce oxygen. Green roofs can also have positive impacts on stormwater management and energy consumption. Cost can be a barrier to implementing a green roof. Several factors influence the cost of a green roof, including design and soil depth, location, and the price of labor and equipment in that market, which is typically lower in more developed markets where there is more experience designing and installing green roofs. The individualized context of each green roof presents a challenge for making broad comparisons and assessments, and focusing only on monetary costs may leave out the social, environmental, and public health benefits green roofs provide. Global comparisons of green roof performance are further challenged by the lack of a shared framework for making such comparisons.

Stormwater management is another option to help mitigate the effect of the urban heat island. Stormwater management is the controlling the water produced by the storm in a way that protects property and infrastructure. Urban infrastructure like streets, sidewalks, and parking lots do not allow for water to penetrate into the earth's surface causing water to flood. By using stormwater management, you can control the flow of the water in ways that can mitigate UHI effect. One way is using a stormwater management technique called pervious pavement system (PPS). This technique has been used in over 30 countries and found to be successful in stormwater management and UHI mitigation. The PPS allows water to flow through the pavement allowing for the water to be absorbed causing the area to be cooled by evaporation.

Green parking lots use vegetation and surfaces other than asphalt to limit the urban heat island effect.

Green infrastructure or blue-green infrastructure refers to a network that provides the “ingredients” for solving urban and climatic challenges by building with nature. The main components of this approach include stormwater management, climate adaptation, the reduction of heat stress, increasing biodiversity, food production, better air quality, sustainable energy production, clean water, and healthy soils, as well as more human centered functions, such as increased quality of life through recreation and the provision of shade and shelter in and around towns and cities. Green infrastructure also serves to provide an ecological framework for social, economic, and environmental health of the surroundings. More recently scholars and activists have also called for green infrastructure that promotes social inclusion and equity rather than reinforcing pre-existing structures of unequal access to nature-based services.

Passive daytime radiative cooling
A passive daytime radiative cooling roof application can double the energy savings of a white roof, attributed to high solar reflectance and thermal emittance in the infrared window, with the highest cooling potential in hot and dry cities such as Phoenix and Las Vegas. When installed on roofs in dense urban areas, passive daytime radiative cooling panels can significantly lower outdoor surface temperatures at the pedestrian level.

Society and culture

History of research
The phenomenon was first investigated and described by Luke Howard in the 1810s, although he was not the one to name the phenomenon. A description of the very first report of the UHI by Luke Howard said that the urban center of London was warmer at night than the surrounding countryside by 2.1 °C (3.7 °F).

Investigations of the urban atmosphere continued throughout the nineteenth century. Between the 1920s and the 1940s, researchers in the emerging field of local climatology or microscale meteorology in Europe, Mexico, India, Japan, and the United States pursued new methods to understand the phenomenon.

In 1929, Albert Peppler used the term in a German publication believed to be the first instance of an equivalent to urban heat island: städtische Wärmeinsel (which is urban heat island in German). Between 1990 and 2000, about 30 studies were published annually; by 2010, that number had increased to 100, and by 2015, it was more than 300.

Leonard O. Myrup published the first comprehensive numerical treatment to predict the effects of the urban heat island (UHI) in 1969. His paper surveys UHI and criticizes then-existing theories as being excessively qualitative.

Aspects of social inequality
Some studies suggest that the effects of UHIs on health may be disproportionate, since the impacts may be unevenly distributed based on a variety of factors such as age, ethnicity and socioeconomic status. This raises the possibility of health impacts from UHIs being an environmental justice issue. Studies have shown that communities of color in the United States have been disproportionately affected by UHI.

There is a correlation between neighborhood income and tree canopy cover. Low-income neighborhoods tend to have significantly fewer trees than neighborhoods with higher incomes. Researchers hypothesized that less-well-off neighborhoods do not have the financial resources to plant and maintain trees. Affluent neighborhoods can afford more trees, on "both public and private property". One reason for this discrepancy is that wealthier homeowners and communities can afford more land, which can be kept open as green space, whereas poorer housing often takes the form of rentals, where landowners try to maximize their profit by putting as much housing density as possible on their land.

Chief heat officers
Beginning in the 2020s, a number of cities worldwide began creating Chief Heat Officer positions to organize and manage work counteracting the urban heat island effect.

Fight against urban heat islands
The fight against urban heat islands (UHI) requires a re-evaluation of urban planning policies and short, medium and long-term strategies. This involves, in particular, the restoration of cool islands, and involves in particular:
to promote passive air conditioning (such as Canadian wells), buffer systems (e.g. Trombe walls), bioclimatic architecture (with bioclimatic pergolas for example) and intelligent insulation, and limit electric air conditioners;
to prefer white or light-colored surfaces and reflective materials so as to increase urban albedo;
to green and reforest towns and their surroundings (e.g. urban green network, green terrace, green wall, etc.), if possible in open ground (more effective than vegetation on roofs). During heatwaves, this greening allows for an average cooling of 2 °C, with local effects around parks of 5 to 6 °C ;
to better conserve and manage rainwater (sponge city, swale systems or wetlands, green roofs and terraces which can re-evaporate this water, evaporation being a cooling factor);
to develop public transport that does not cause smog;
to change habits (modification of working hours, naps, etc.) depending on heat peaks ;
to ensure that planning requirements guarantee an urban form where air circulation is optimal, by adapting good urban planning practices and regulations to local conditions (for example, passive cooling systems, natural thermal regulation systems in buildings inspired by the circulation of air in termite mounds, a narrow street can be a " calorie trap " if it includes hot sources (boilers, vehicles, factories, air conditioners, etc.), and on the contrary a guarantee of freshness in a very hot country where it protects from the heat of the sun. Indeed, the design of current cities "breaks the circulation of air" according to Anne Ruas, researcher at Ifsttar.

In France, the EPICEA study focused on climate forecasting for the Paris metropolitan area, "the specific study of the extreme situation of the 2003 heatwave" and the links between urban fabric (geometry, materials, etc.) and urban climate, as well as on the evaluation of the "impact of urban planning on meteorology". It used the simulation of heat plumes and urban breezes according to architectonics (street width, height and shape of buildings, etc.) and materials (albedo, etc.) to cross-reference the models with excess mortality data (from InVS and Inserm, CépiDc), in order to propose "adaptation strategies for urban areas". Greening urban spaces (walls, terraces, pergolas, etc.) and controlling certain anthropogenic heat emissions (through insulation and albedo or energy savings and air conditioning control) are the two parameters on which it is easiest to act quickly. Urban geometry is in fact relatively fixed on human timescales, particularly in Paris.

In the 2000s, research and development work considered cool pavements or cold roads, based on two principles: either light-colored materials reflect sunlight (but with possible problems of glare and heating of the built environment, and aggravating the production of tropospheric ozone if the material also reflects solar UV rays); or by absorbing water and evaporating it (evaporation cools the air, but has the disadvantage of water consumption which makes this solution inapplicable in arid areas; moreover, sea water or salinized water cannot be used, because salt crusts would quickly clog the pores of the material.

Measuring global warming
Some authors have argued that the relevance of climate data considered as indices of global warming is biased by urban heat islands, at least if they are attributed entirely to a cause such as greenhouse gas emissions.

The Intergovernmental Panel on Climate Change (IPCC), based on a 1990 Letter to Nature, concluded in its third report that their effect could not exceed 0.05 degrees Celsius at the global level. A 2008 study estimates the contribution of urban heat islands to the warming measured in China at 0.1 °C per decade, between 1950 and 2004, for a total increase of 0.81 °C. In already industrialized countries, the effect of urbanization has been constant for decades. According to the three authors, the effect of urban heat islands therefore represents the majority of the global warming measured so far in China but not in industrialized countries.

Influence on climate and physical effects
The sensible heat flux over an urbanized area is greater than the heat flux in the surrounding countryside. Thus, in Paris, the sensible heat flux is 25 to 65 W/m 2 higher than in the surrounding rural suburbs. Thus, it is 20 to 60% higher than the "normal" heat flux.

In cities, the temperature can be 10 °C higher than in surrounding areas. This can also cause a significant increase in precipitation.

Examples

United States
Bill S.4280, introduced to the U.S. Senate in 2020, would authorize the National Integrated Heat Health Information System Interagency Committee (NIHHIS) to tackle extreme heat in the United States. Successful passage of this legislation would fund NIHHIS for five years and would instate a $100 million grant program within NIHHIS to encourage and fund urban heat reduction projects, including those using cools roofs and pavements and those improving HVAC systems. As of July 22, 2020 the bill has not moved past introduction to Congress.

The city of New York determined that the cooling potential per area was highest for street trees, followed by living roofs, light covered surface, and open space planting. From the standpoint of cost effectiveness, light surfaces, light roofs, and curbside planting have lower costs per temperature reduction.

Los Angeles
A hypothetical "cool communities" program in Los Angeles has projected in 1997 that urban temperatures could be reduced by approximately 3 °C (5 °F) after planting ten million trees, reroofing five million homes, and painting one-quarter of the roads at an estimated cost of US$1 billion, giving estimated annual benefits of US$170 million from reduced air-conditioning costs and US$360 million in smog related health savings.

In a case study of the Los Angeles Basin in 1998, simulations showed that even when trees are not strategically placed in these urban heat islands, they can still aid in minimization of pollutants and energy reduction. It is estimated that with this wide-scale implementation, the city of Los Angeles can annually save $100M with most of the savings coming from cool roofs, lighter colored pavement, and the planting of trees. With a citywide implementation, added benefits from the lowering smog-level would result in at least one billion dollars of saving per year.

Los Angeles TreePeople is an example of how tree planting can empower a community. TreePeople provides the opportunity for people to come together, build capacity, community pride and the opportunity to collaborate and network with each other.

Los Angeles has also begun to implement a Heat Action Plan to address the city's needs at a more granular level than the solutions provided by the state of California. The city uses the LA Equity Index in an effort to ensure that the effects of extreme heat are mitigated in an equitable manner.

Virginia
In 2021, Climate Adaptation Planning Analysis (CAPA) received funding from the National Oceanic and Atmospheric Administration to conduct Heat Mapping across the United States. Ten areas from Virginia – Abington, Arlington, Charlottesville, Farmville, Harrisonburg, Lynchburg, Petersburg, Richmond, Salem, Virginia Beach and Winchester – participated in the heat watch campaign. This campaign consisted of 213 Volunteers brought together by campaign organizers who made 490,423 Heat Measurements across 70 Routes total. After taking measurements throughout the day, equipment and data was sent back to CAPA where it was analyzed using machine learning algorithms. After analysis of the data, CAPA came back together with campaign organizers from each area to discuss potential plans for each town in the future.

New York
New York City implemented its "Cool Neighborhoods NYC" program in 2017 intending to mitigate the effects of extreme urban heat. One of the plan's ambitions was to increase funding for the city's Low-Income Home Energy Assistance Program. Specifically, the plan sought to increase funding for cooling solutions for lower-income families.

India
Several cities in India experience significant urban heat island effects due to rapid urbanization, loss of green cover, and extensive concretization. A report by The Hindu highlights that metropolitan areas like Delhi, Bengaluru, Chennai, Jaipur, Ahmedabad, Mumbai, and Kolkata have seen temperature differences ranging from 1 °C to 6 °C compared to their rural surroundings. These urban heat islands not only increase the local temperatures but also exacerbate the impacts of heatwaves, leading to higher energy consumption for cooling and posing health risks to vulnerable populations.

Mumbai, India's financial hub and one of the most densely populated cities globally, is significantly affected by the urban heat island effect. Rapid urbanization, extensive concretization, and loss of green spaces have led to higher temperatures in the city compared to its surroundings. According to a report, Mumbai is projected to spend twice as much as New York City to manage urban heat generated due to concretization. This increased expenditure highlights the severity of the urban heat island effect in Mumbai and its impact on the city's infrastructure and residents.

France
Recent models (2012) by Météo-France and Paris (trend scenario, i.e. "moderately pessimistic" concerning global greenhouse gas emissions) confirm that the number and severity of heatwaves are expected to increase by 2100 (by 2 to 4 °C by the end of the century compared to the 1971-2006 average), especially in July-August (3.5 to 5 °C more than normal), with approximately 12 times more heatwave days per year. In the heat dome of the Île-de-France region, neighborhoods and districts will be more or less exposed, depending on the width of the streets, the height, color and type of buildings present, the vegetation cover, the proximity or presence of water ; The 2nd, 3rd, 8th, 9th, 10th and 11th arrondissements are warming up the most (as in 2003 with 4 to 7 ° C more than in the inner suburbs, at the end of the night, and with a difference of 2 to 4 ° C depending on the Parisian arrondissements). A "heat plume" effect also modifies the geography of the hot bubble. Reducing the temperature by a few degrees could improve the quality of life and save lives; in 2003, a few degrees more than the average led to an excess mortality of 15,000 deaths in France and nearly 70,000 in Europe.

Regarding possible urban adaptations in Paris, according to the same models:
for the dense city center, vegetation and an increase in albedo would only lower the temperature by 1 °C on average for the duration of a heatwave and by 3 °C at best locally at a given time) ;
the revegetation of the bare soils of Paris associated with a rate of 50% of roads more than 15 meters wide covered by trees (1,160 hectares in total) would allow a fall of 3 to 5 °C in the daytime temperature, as long as the flora does not lack water (because it is evapotranspiration which cools the air the most) ;
humidification of the roads (watering 14 hours/day) of the capital via its non-potable water network would contribute to reducing dust, but would have a lesser effect on the temperature (−0.5 ° C on average between 8 andAugust 13, 2003, with at best −1 to −2 °C during the day). Misting would probably be more effective, but would inject microbes into the air if it used non-potable water. However, humidifying roadways allows for temperature reductions in areas where it is difficult or even impossible to increase the rate of vegetation (particularly in the 2nd, 9th and 10th arrondissements) 


Sourced from Wikipedia

2020年5月7日星期四

Objective abstraction

Objective abstraction was a British art movement. Between 1933 and 1936 several artists later associated with the Euston Road School produced almost or totally abstract paintings executed in a free painterly manner. Along with Tibble and Graham Bell, Moynihan produced the most abstract of these. This example is from Objective Abstraction's middle phase, when definite marks and longer strokes had given way to denser textures. In his words: 'the gradual thickening of the paint was ... a kind of build-up as a result of correction and suggestion'. He was 'continually aware of the lung movement of paint, its ability to breathe and move upon the surface of the canvas'.

History
Objective abstraction was part of the general ferment of exploration of abstraction in Britain in the early 1930s. The paintings produced by the group evolved in an improvisatory way from freely applied brushstrokes.

Objective abstraction was a form of abstract art developed by a group of British artists in 1933. Experimentation was prevalent in British art at the time.

The main figures were Graham Bell, William Coldstream, Edgar Hubert, Rodrigo Moynihan and Geoffrey Tibble.

The movement was short-lived lasting only a few years. Many of the artists involved went on to be part of the realist Euston Road School.

Method
William Townsend told the Tate Gallery that 'the style originated with Geoffrey Tibble in the latter half of 1933. It was immediately taken up by Rodrigo Moynihan  and at the same time or shortly after by Edgar Hubert'. According to Townsend, early paintings by the group were derived from external objects but they became increasingly abstract.

The more abstract paintings, that came to represent the movements style, were created using improvised freely applied brushstrokes. Geoffrey Tibble described them as 'not abstracted from nature, and which made no reference to and had no associations with anything outside themselves  the picture was an object in its own right' (Bowness, 1960:198).

Exhibitions
In 1934, the exhibition Objective Abstractions was held at the Zwemmer Gallery showing the group's work, except Hubert's. The exhibition also included work by more representational artists, Ivon Hitchens, Victor Pasmore, and Ceri Richards. On the other hand, works by non objective abstraction artists Ivon Hitchens, Victor Pasmore, and Ceri Richards, were added to the show by the gallery’s director. Moynihan was inspired by the brushwork in the late paintings of Joseph Mallord William Turner and Claude Monet.

Moynihan exhibited a number of non-representational works between 1934 and 1937, all with the title ‘Painting’ or ‘Drawing’; His work also shows that the work was partly repainted after that time; there were originally more sharply defined contrasts of tone with dark areas in the centre and, more clearly than at present, in the lower corners.

Mr Townsend distinguishes three phases in the development of Moynihan's and Tibble's non-representational work in the 1930s: the first was characterized by broad, loosely painted brush-strokes, as in the examples reproduced in the 1934 Zwemmer Gallery catalogue; after the exhibition this was replaced by a much more deliberate style, only a few paintings being worked on over a long period to produce a lighter and more even tone and a denser texture obscuring the individual brush-strokes; in 1936 there was a return to a more rapid looser technique. The Tate Gallery's picture belongs to the second phase and was probably begun in 1935, though not ready to exhibit at the London Group of October–November that year (its subsequent reworking has been mentioned above): it is similar in style both to a painting in the collection of W. W. Winkworth, which was purchased at the London Group exhibition of October–November 1935, and to the larger work, signed and dated 1936, still in the possession of the artist.

The catalogue of the 1934 exhibition at the Zwemmer Gallery includes the artists' answers to a number of questions. Moynihan, in reply to the question ‘Do you consider your paintings “impressionist”?’, states that they ‘have more in common with the impressionist technique whereby painting identifies itself with, and derives from, its means, than with a system in which the artist imposes upon the canvas a preconceived idea;... the evolution is intimately bound up with the canvas and medium’. William Townsend, in a letter to The Listener of 18 April 1934 which he wrote independently but which was approved by Geoffrey Tibble, defined the use of the word ‘Objective’: ‘the painting is to be regarded as having from the first touch that right to exist independently of the painter himself on which later it will depend for any significance it may have’.

2020年3月20日星期五

History of Sasanian Armenia

Sasanian Armenia, also known as Persian Armenia and Persarmenia (Armenian: Պարսկահայաստան – Parskahayastan), may either refer to the periods where Armenia (Middle Persian: 𐭠𐭫𐭬𐭭𐭩‎ – Armin) was under the suzerainty of the Sasanian Empire, or specifically to the parts of Armenia under its control such as after the partition of 387 AD when parts of western Armenia were incorporated into the Byzantine Empire while the rest of Armenia came under Sasanian suzerainty whilst maintaining its existing kingdom until 428.

In 428, Armenian nobles petitioned Bahram V to depose Artaxias IV (r. 422); Bahram V (r. 420–438) abolished the Kingdom of Armenia and appointed Veh Mihr Shapur as marzban (governor of a frontier province, "margrave") of the country, which marked the start of a new era known as the Marzpanate period (Armenian: Մարզպանական Հայաստան – Marzpanakan Hayastan), a period when marzbans, nominated by the Sasanian emperor, governed eastern Armenia, as opposed to the western Byzantine Armenia which was ruled by several princes, and later governors, under Byzantine suzerainty. The Marzpanate period ended with the Arab conquest of Armenia in the 7th century, when the Principality of Armenia was established. An estimated three million Armenians were under the influence of the Sasanian marzpans during this period.

The marzban was invested with supreme power, even imposing death sentences; but he could not interfere with the age-long privileges of the Armenian nakharars. The country as a whole enjoyed considerable autonomy. The office of Hazarapet, corresponding to that of Minister of the Interior, public works and finance, was mostly entrusted to an Armenian, while the post of Sparapet (commander-in-chief) was only entrusted to an Armenian. Each nakharar had his own army, according to the extent of his domain. The "National Cavalry" or "Royal force" was under the Commander-in-chief. The tax collectors were all Armenians. The courts of justice and the schools were directed by the Armenian clergy. Several times, an Armenian nakharar became Marzpan, as did Vahan Mamikonian in 485 after a period of rebellion against the Iranians.

Three times during the Marzpanic period, Iranian kings launched persecutions against Christianity in Armenia. The Iranians had tolerated the invention of the Armenian alphabet and the founding of schools, thinking these would encourage the spiritual separation of Armenia from the Byzantines, but on the contrary, the new cultural movement among the Armenians proved to be conducive to closer relations with Byzantium.

Background
Christianity became the state religion of Armenia in 301. In 367 Armenia was divided between Sasanian Iran and the Roman Empire. The former established control in Eastern Armenia after the fall of the Arshakuni Armenian kingdom in 428.

History

Marzbanate (428–646)
In 428, Armenian nobles, nakharar, dissatisfied with the rule of Artaxias IV petitioned emperor Bahram V to depose him. Bahram V abolished the Kingdom of Armenia and appointed Veh Mihr Shapur as marzban (governor of a frontier province, "margrave") of the country.

In 465, Adhur Gushnasp was appointed by the Sasanian emperor Peroz I (r. 459–484) as the marzban of Armenia, replacing Adhur Hormizd. In 475, the Mamikonian princess Shushanik, was murdered by her husband Prince Varsken, a recent convert to Zoroastrianism, because she refused to convert and wanted to stay Christian. Varsken was then executed by Vakhtang I, king of Iberia.

Peroz I, eager to avenge Varsken, sent his general Shapur Mihran to Iberia. Vakhtang then appealed to the Huns and the Armenian nobles, citing solidarity between Christians. After carefully weighing the decision, the Mamikonian prince Vahan Mamikonian agreed to revolt against the Sasanians. He defeated and killed Adhur Gushnasp, and thereafter declared Sahak II Bagratuni as the new marzban. He also kept repelling several Sasanian counter-attacks.

In 482, Shapur Mihran began to become a big threat to the security of Iberia, which made Vakhtang request Armenian aid. Vahan and Sahak shortly arrived to Iberia at the head of a big army, but were defeated in Akesga, where Sahak was killed. Vahan fled with the remnants of the Armenian army into the mountains, where he led guerrilla actions against the Sasanians, while Shapur Mihran managed to regain control of Armenia. However, Shapur Mihran was shortly ordered to return to the Sasanian capital of Ctesiphon. Vahan quickly used the opportunity to regain control of Armenia.

In the spring of 484, however, Shapur Mihran returned as the head of a new army and forced Vahan to flee to refuge near the Byzantine frontier, at Tao and Taron. During the same period, the Sasanian noble Zarmihr Karen from the Karenid family, was successful in another campaign against the Armenians, and managed to capture several of them, including noblemen from the Kamsarakan family. Zarmihr shortly delivered the Armenian captives to Shapur Mihran, who delivered them to Izad Gushnasp, promising the Armenian captives to make Peroz spare them.

However, an unexpected event changed the course of events: the death of the Sasanian king Peroz I in 484 in war against the Hephthalites, causing the withdrawal of the Sasanians in Armenia and recovery of Dvin and Vagharshapat. Struggling to suppress the revolt of his brother Zarir, Peroz's successor, Balash (r. 484-488), needed the help of the Armenians: in exchange for military support, he agreed to sign the Nvarsak Treaty, which granted religious freedom to the Christians and the prohibition of Zoroastrianism in Armenia, including much greater autonomy for the nakharar. Vahan was also recognized as sparapet and the property of the Mamikonian family and its allies were returned.

Between 515-516, several Hunnic tribes kept making incursions into Armenia—the Armenian nobleman Mjej I Gnuni then decided to organize a counter-attack, where he successfully managed to repel them. As a reward, Kavadh I appointed him as the marzban of Armenia in 518. During this governorship, Mjej maintained religious peace. In 527, he repelled several other Hunnic invasions. In 548, he was succeeded by Gushnasp Bahram.

Chihor-Vishnasp, a member of the Suren family and a relative of Khosrow I himself, was in 564 appointed as marzban. During this period, the Armenian aristocracy was split between two parties, the national one which was headed by a member of the Mamikonian family, and a pro-Sasanian one, which was headed by a member of the Siunia family.

Chihor Vishnasp not only harshly treated the Christian Armenians who were suspected of secretly siding with the Byzantines, but also did the same with the rest of the Christian Armenian population. Claiming to exploit on the command of the king, he persecuted the Christian Armenians and even built a fire-temple in Dvin. These actions soon resulted in a massive uprising in late 571 or early 572, which was led by Vardan III Mamikonian. On 23 February 572, the Armenian rebels seized Dvin, and had Chihor-Vishnasp killed.

The Armenians and the Achaemenid Empire
After the fall of the Medo Empire in 550 BC. C. Cyrus, the leader of the Persians took control of the empire and conquered Asia Minor and Mesopotamia. Cyrus's son Cambyses followed his father in the Egyptian campaign. Armenia became a dependency of Persia.

Armenian cavalry and infantry troops had taken part in the conquest of Cyrus of Lydia in 546 and of Babylon in 539. A rebellion of ten nations - one of them Armenia - broke out against Persia during the reign of Darius I (522 - 486).

The Armenians and the Sassanid Empire
The Armenians adopted Christianity as the official state religion in the year 301. Armenia was divided between the Sassanid Empire of Persia and the Roman Empire. The first established control in eastern Armenia after the fall of the Armenian kingdom Arsácida in 428.

Vartan Mamikonian
With the increase in conflicts between Romans and Sassanids, Yazdegerd II began to see Christianity as a political threat to the cohesion of the Persian empire. The conversion to Christianity by the Armenians was of particular interest to him. After a successful invasion of the Eastern Roman Empire, Yazdegerd summoned the Armenian nobles to Ctesiphon and converted them to Zoroastrianism. This outraged the Armenian population, and under Vartan Mamikonian leadership an army of 66,000 Armenians rebelled against the Sassanid Empire. Yazdegerd quickly quelled the rebellion at the Battle of Avarayr.

Consequences
The Persians' military success over Armenia ensured that it would remain part of the Sassanid Empire for several centuries. However, the Armenian resistance did not end until the Treaty of Nvarsak, which guaranteed Armenia more freedom under Sassanid rule.

The Armenians and the Safavid Empire
Due to its strategic importance, Armenia was constantly disputed and changed hands on several occasions and successively between the rule of Persia and the Ottomans. In the Turkish-Persian wars, it should be noted that Yerevan changed hands fourteen times between 1513 and 1737.

In 1604, Shah Abbas I used a military strategy in which he destroyed everything the Ottomans had to subsist - farms, houses and scorched earth, in the Ararat valley. The ancient Armenian town of Julfa, in the Nakhichevan province was taken at the beginning of the invasion. From there, Abbas's army occupied Araratian across the plain. The shah followed a careful strategy, advanced and retired when the occasion demanded, determined not to risk his company in a direct confrontation with the strongest enemy forces.

When Kars was besieging, he learned of the arrival of a large Ottoman army, commanded by Djghazadé Sinan Pasha. They were ordered to retreat, but the enemy denied the possibility of self-resupply, ordered the destruction of the largest Armenian cities and farms on the plain. As part of this plan, the population was ordered to accompany the Persian army on its retreat. Some of the 300,000 people were left to fend for themselves on the banks of the Aras River. Those who tried to resist mass deportation were killed instantly. The Shah had ordered the destruction of the only bridge, so that people were forced to cross the rushing waters, where a large number of Armeniansthey perished drowned, or swept away by the currents, before reaching the opposite bank. This was only the beginning of his ordeal. An eyewitness, Guyan's father, describes the plight of the refugees in this way:

It was not just the winter cold that caused torture and death to deportees. The greatest suffering came from hunger. The provisions that the deportees had brought with them were soon consumed... The children were crying for food or milk, none of which existed, because the women had dry breasts even from hunger... Many women, hungry and exhausted, he would leave his hungry children on the side of the road, and they followed their tortuous path. Some may go to the nearby forests in search of something to eat. Usually, he doesn't come back. Many times those who died served as food for life.

Unable to maintain his army on the desolate plain, Sinan Pasha was forced to win in Van. Armies that were sent in pursuit of the Shah in 1605 were defeated, and Abbas in 1606 had recovered all the territory that he lost to the Turks early in his reign. The tactic of razing land tactics had worked, albeit at a terrible cost to the Armenian people. Of the 300,000 deportees, it is estimated that less than half survived the Isfahan march. In the conquered territories, Abbas established the khanate of Yerevan, a Muslim principality under the rule of the Safavid Empire. Armenians made up less than 20% of its population as a result of the deportation of much of the Armenian populationof Ararat valley and the surrounding region in 1605 by Shah Abbas I.

Vardan Mamikonian
Sasanian king Yazdegerd II began to view Christianity in the Northern lands as a political threat to the cohesiveness of the Iranian empire. The dispute appears to be based on Iranian military considerations of the time given that according to Acts 2:9 in the Acts of the Apostles there were Persians, Parthians and Medes (all Iranian tribes) among the very first new Christian converts at Pentecost and Christianity has had a long history in Iran as a minority religion, dating back to the very early years of the faith. Nevertheless, the conversion to Christianity by Armenians in the North was of particular concern to Yazdegerd II. After a successful invasion of the Eastern Roman Empire, Yazdegerd began summoning Armenian nobles to Ctesiphon and reconverted them to Zoroastrianism (a faith many Armenians shared with Iranians prior to Christianity). This upset the Armenian population, and under the leadership of Vardan Mamikonian an army of 66,000 Armenians rebelled against the Sasanian empire. Yazdegerd quickly subdued the rebellion at the Battle of Avarayr.

Nvarsak Treaty
The military success of the Iranians ensured that Armenia would remain part of the Sasanian empire for centuries to come. However, Armenian objections did not end until the Nvarsak Treaty, which guaranteed Armenia more freedom and freedom of religion (Christianity) under Sasanian rule.

Sasanian coins produced in Armenia
Sasanian government had produced gold, silver and bronze coins in Armenia. 813 of these coins were found in 34 regions in Armenia; being most of them found in Dvin (ancient city) and Gyumri. Most of these coins were silver coins.

Viceroys

Sasanian kings of Armenia

TenureKingNotes
252/3-272Hormizd ISasanian prince, nominated by his father Shapur I.
272-299NarsehSasanian prince, nominated by his brother Hormizd I.

Marzbans of Armenia
TenureKingNotes
252/3-272Hormizd ISasanian prince, nominated by his father Shapur I.
272-299NarsehSasanian prince, nominated by his brother Hormizd I.
Marzbans of Armenia
TenureMarzbanNotes
428-442Veh Mihr ShapurIranian grandee, nominated by Bahram V.
442-451Vasak, prince of SyunikArmenian nobleman, nominated by Yazdgerd II.
451-465Adhur Hormizd (in Armenian sources: Adrormizd)Iranian grandee, nominated by Yazdgerd II.
465-481Adhur Gushnasp (in Armenian sources: Arderveshnasp)Iranian grandee, nominated by Peroz I.
481-482Sahak II BagratuniArmenian nobleman, elected by the rebellious Armenian nobles. Killed at the Battle of Akesga.
482-482Shapur MihranIranian military occupation.
482-483Vahan I MamikonianHead of provisional government.
483-483Zarmihr KarenIranian military occupation.
483-484Shapur of RayIranian grandee, nominated by Peroz I.
Cyril Toumanoff suggests a marzpan named Andigan for the same period.
484-505/510Vahan I Mamikonian (2nd term)Armenian nobleman, nominated by Peroz I.
505-509 or 510-514Vard Mamikonian ("Vard the Patrician")Brother of Vahan I, recognized as marzpan by Kavadh I.
11 yearsSeveral Iranian marzpans persesAccording to Samuel of Ani: "After the patrician Vard, brother of Vahan, Iranian marzpans governed Armenia for 11 years... The government of Armenia passed then to Mjej of the Gnuni family, who exercised it for 30 years".
518-548Mjej I GnuniMentioned by Cyril Toumanoff and Gérard Dédéyan, but not included by René Grousset.
548-552 or 552-554Gushnasp Bahram 
552-560 or 554-560Tan-Shapur 
560-564Varazdat 
564-572Chihor-Vishnasp 
572-573Vardan III MamikonianLeader of anti-Iranian rebellion.
572-574Golon MihranIranian general tasked by Khosrau I with subduing the revolt. Cyril Toumanoff substitutes him and Vardan with Vardan-Gushnasp.
573-577Vardan III MamikonianUnder Byzantine protectorate.
For the same period, Krikor Jacob Basmadjian a Cyril Toumanoff have Philip, prince of Syunik.
577-580TamkhosrauIranian grandee, nominated by Khosrau I.
580-581Varaz VzurIranian grandee, nominated by Hormizd IV
581-582/588PahlavIranian grandee, nominated by Hormizd IV.
582/588-588/589FrahatIranian grandee, nominated by Hormizd IV.
588/589-590Hrartin (Fravardin)Iranian grandee, nominated by Hormizd IV.
590-591Musel II MamikonianInstalled by the Byzantines.
592-605VindatakanThese five marzpans are mentioned by Cyril Toumanoff.
Nakhvefaghan
Merakbout
Yazden
Boutmah
604-611 or 616Smbat IV BagratuniChristian Settipani records him as marzpan from 599 to 607. He is not mentioned as marzpan by Toumanoff. René Grousset holds that Khosrau II named him marzpan following his victories in Hyrcania, ca. 604, and adds that he possibly continued in office until his death in 616-617. However, he also mentions three other marzpans over the same period (see following).
611-613ShahrayeanpetMarzpan at Dvin, in eastern Armenia, along with Shahin Vahmanzadegan as pahghospan in western (former Byzantine) Armenia
613-613ParshenazdatIranian grandee, nominated by Khosrau II.
616-619Namdar-GushnaspIranian grandee, nominated by Khosrau II.
619-624Shahraplakan (Sarablagas)Iranian grandee, nominated by Khosrau II.
624-627RotshvehanIranian grandee, nominated by Khosrau II.
627-628 A large part of Armenia reverted to Byzantine control.
ca. 628Varaztirots II BagratuniArmenian nobleman, named marzpan by Kavadh II for the portions of Armenia remaining under Iranian rule. Following the onset of the Muslim conquest of Iran, Varaztirots aligned himself with the Byzantines.
630-635Mjej II GnuniArmenian nobleman, named governor of Armenia by the Byzantine emperor Heraclius.
635-638David SaharuniArmenian nobleman, he murdered Mjej and proclaimed himself governor. He was recognized by Heraclius, who named him kouropalates and ishkhan of Armenia.
638-643 No central authority.
643-645Theodore Rshtuni 
645/646Varaztirots II BagratuniFollowing the complete collapse of Iran, he was named Prince of Armenia by the Byzantines, but died before being formally invested

Modern era
Throughout the xvi th and beginning of the xvii th centuries, Armenia is the battlefield on which confront the Ottomans and Persians, passing alternately under the domination of one or the other. The treaty of Qasr-i-Chirin puts an end to this situation in 1639 and grants Eastern Armenia to Persia. The country is strongly depopulated, following the decision of Abbas IPersian (performed 1604 - 1605) to deportof Armenians in the region of Isfahan, in order to create a center of commerce in New Julfa, but also to clear the area in front of the Ottoman armies and prevent their supply.

At the beginning of the xviii th century, following the decline of the Persian Safavid and first Russian incursions in the Caucasus, the Ottomans decided to react and walk on Persian Armenia; Yerevan thus falls on June 7, 1724, but Karabagh and Zanguezour resist under the direction of David Bek; it was only in 1730 that the Persian troops managed to retake the region. In 1747, the death of Nadir Shah, the Persian Armenia is divided between three khanates relatively autonomous, the khanates of Yerevan to Nakhchivan and Karabakh.

The beginning of the xix th century saw the little Persian Armenia to fall slightly to the Russians. The Russo-Persian War of 1804-1813, concluded by the Treaty of Golestan, gave rise to the taking of the Karabakh Khanate. As for the Khanates of Yerevan and Nakhichevan, they fell at the end of the Russo-Persian War of 1826-1828, ratified by the Treaty of Turkmanchai. Persian Armenia then made way for Russian Armenia.

History of Byzantine Armenia

Byzantine Armenia, sometimes known as Western Armenia, is the name given to the parts of Kingdom of Armenia that became part of the Byzantine Empire. The size of the territory varied over time, depending on the degree of control the Byzantines had over Armenia.

The Byzantine and Sassanid Empires divided Armenia in 387 and in 428. Western Armenia fell under Byzantine rule, and Eastern Armenia fell under Sassanid control. Even after the establishment of the Bagratid Armenian Kingdom, parts of historic Armenia and Armenian-inhabited areas were still under Byzantine rule.

The Armenians had no representation in the Ecumenical Council of Chalcedon in 451, due to their struggle against the Sassanids in an armed rebellion. For that reason, there appeared a theological drift between Armenian and Byzantine Christianity.

Regardless, many Armenians became successful in the Byzantine Empire. Numerous Byzantine emperors were either ethnically Armenian, half-Armenian, part-Armenian or possibly Armenian; although culturally Greek. The best example of this is Emperor Heraclius, whose father was Armenian and mother Cappadocian. Emperor Heraclius began the Heraclean Dynasty (610–717). Basil I is another example of an Armenian beginning a dynasty; the Macedonian dynasty. Other great emperors were Romanos I, John I Tzimiskes, and Nikephoros II.

History
Origins
Lucullus and Pompey had pushed the influence of Rome to Armenia around 66 BC. AD. Tigrane II, the Armenian king of that time, was forced to pay tribute to the Romans and he lost many territories. Armenia had become a buffer state between Rome and Arsacid Persia. After the death of Tigrane II, the Roman general Marc Antoine tried to give the kingdom to one of his sons. The general's defeat at Actium in 31 BC. AD, however, ended his ambition to leave the kingdomto his descendants. Artaxias II, grandson of Tigrane, succeeds with the help of the Persians, to regain control of the territory. Towards the end of the 1 st century BC, internal conflicts between the pro-Roman and propersian Armenians precipitated the Artaxiad dynasty towards its end in 10 BC. AD. In the first century, Armenia was politically divided between the Roman Empireand Arsacid Persia. To ensure they have some control over Armenia, the Romans offer a compromise. Aware of the fact that the Persians are very influential in Armenia and that the Armenian monarchy is of Persian origin, the Romans propose to leave this Persian monarchy at the head of the country but they want to give the crown to the king. In this way, the Arsacids retain their power over Armenia and Rome made it a protectorate. The situation is quite stable until iv th century despite some turbulence on both sides of the border.

The iv th to the vii th century
In 387, the Roman situation was not at its best due to the Germanic invasions. In addition, Persia knows the emergence of a new dynasty, the Sassanids. A certain influence on Armenia must be kept. This is why the two powers agree on a division of the kingdom. Thus, the region becomes three new political entities: the imperial province of Armenia minor located west of the Euphrates, the kingdom of Great Armenia located east and the satrapiesArmenian women in the South. The satrapies and the kingdom of Great Armenia are under Persian influence and represent 4/5 of the historic Armenian territory. The imperial province is headed by a Comes Armeniae, a governor of species, until the reign of Justinian I to vi th century. During his reign, Justinian increased the size of the imperial province by integrating part of the territory of the southern satrapies and part of the Pont region in Anatolia. This territorial expansion has resulted in the creation of 4 new territorial entities, the provinces of Armenia I to IV 5. These Byzantine provinces reached their territorial apogee during the reign of the Emperor Mauritius, which extended Armenian territory to the east near Dvin and to the northwest near Lake Van by the peace treaty of 591.

The Armenian provinces were finally conquered in the middle of the vii th century by the Arabs after increasing tensions between Byzantium and Armenia. In fact, Byzantium tried to integrate the Armenian Church into its own and to impose its worship and traditions. This attempt at religious imperialism ignited the anger of the local nobles as well as that of the clergy. So when the Arabs marched on the provinces, local forces did not offer much resistance.

Arab domination and the revival of Armenian royal power
The vii th century marked a change not only for Armenia but for almost Near and Middle East. A new political force, the Arabs overthrow the Sassanid power in Persia and snatch Syria and Egypt from the Byzantines. This new power allows significant social changes in Armenia. At the start of the Arab presence taxes were low and social control was moderate. The occupiers recruited Armenian horsemen to protect themselves from attacks from the Khazars in the North Caucasus. In addition, Armenia, Iberiaand Caucasian Albania are politically reorganized into a single province called Armîniya. During this period, the provincial governor bore the title of ostikan. The western border of Arminiya was militarized and turned against Byzantium. If this period is marked by a cultural development and renewal, the Arab government of the Umayyads and later the Abbasids has always been very difficult to establish legally on the territory of Armenia. Regular revolts took place against Arab administrators due to tightening of power. Then, before the character hotter insurgencies, the Caliph Abbasid recognizes the representative of Bagratid family, Ashot I st as ruler of Armenia and releases nakharars who revolted. Indeed, the ix th century, the Abbasid Caliphate enters a difficult period and Byzantium began an expansion to the East. During the same period, Ashot I first became ruler of the dynasty Bagratid north and south during this time, the arçrouni dynasty control areaVaspourakan. This short national revival ends during the second part of the x th century, when the Byzantine Empire extends again its territory to Armenia and reinstate the imperial court.

x th and xi th centuries
If the first part of the x th century was characterized by the revival of royal power in Armenia, the second part however, marks the return of the Byzantines in Armenia. By the end of the x th century, the Bagratuni kingdom and arçrouni of Great Armenia fell one after the other into the hands Byzantine: the Taron in 968, the Tayk in 1001, the Vaspurakan in 1021 or 1022, Ani in 1045, Kars in 1065; only the Lorri escapes the emperors. If the Taron becomes in 968, an imperial province, it is not at this time of a pure and simple assimilation. Indeed, the Emperor Jean Tzimiskès and the Bagratide king Ashot III collaborate during this period. During the reign of Basil II, the tone changes and he goes forward to assimilate the other Armenian territories. The aggressiveness of the Byzantine invasion forces King Arçrouni Gagik IIto abdicate and entrust his lands to the Byzantines. Most of the Armenian territories were integrated into imperial themes such as that of Iberia and Mesopotamia. This Byzantine domination, which sees most of the Armenian nobility migrating to Anatolia and Cilicia 16, is short-lived: the Seljuk threat is indeed on the horizon.

The first foray occurred in 1045 - 1046, followed by many others, and, theAugust 16, 1064, sultan Alp Arslan takes Ani. Most of Armenia then succumbed to the Seljuk assaults, with the exception of Lorri and Siounie; the battle of Manzikert, in 1071, consecrates the conquest of Armenia, just like the geographical rupture of Byzantium with this country. The country is then integrated into the Persian Seljuk and entrusted to various emirs based notably Dvin and Ganzak, the last islands (Lorri and Siounie) succumbing to the xii th Century.

Armenian military in the Byzantine Army
Armenia made great contributions to Byzantium through its troops of soldiers. The empire was in need of a good army as it was constantly being threatened. The army was relatively small, never exceeding 150,000 men. The military was sent to different parts of the empire, and took part in the most fierce battles and never exceeded 20,000 or 30,000 men. From the 5th century forwards the Armenians were regarded as the main constituent of the Byzantine army. Procopius recounts that the scholarii, the palace guards of the emperor, "were selected from amongst the bravest Armenians".

Armenian soldiers in the Byzantine army are cited during the following centuries, especially during the 9th and the 10th centuries, which might have been the period of greatest participation of the Armenians in the Byzantine army. Byzantine and Arab historians are unanimous in recognizing significance of the Armenians soldiers. Charles Diehl, for instance, writes: “The Armenian units, particularly during this period, were numerous and well trained.” Another Byzantine historian praises the decisive role which the Armenian infantry played in the victories of the Byzantine emperors Nicephorus Phocas and John Tzimiskes.

At that time the Armenians served side by side with the Norsemen who were in the Byzantine army. This first encounter between the Armenian mountain-dwellers and the Norse has been discussed by Nansen, who brings these two elements closer to each other and records: “It was the Armenians who together with our Scandinavian forefathers made up the assault units of Byzantine.” Moreover, Bussel underlines the similarities in the way of thinking and the spirit of the Armenian feudal lords and the northern warriors. He claims that, in both groups, there was a strange absence and ignorance of government and public interest and at the same time an equally large interest in achieving personal distinctions and a loyalty towards their masters and leaders.

Armenian Emperors of Byzantium
The partition of the Roman Empire between the two sons of the Emperor Theodosius was soon followed by a predominance of foreign elements in the court of Byzantium, the eastern half of the divided world. The proximity of this capital of the East to Armenia attracted to the shores of the Bosporus a great number of Armenians, and for three centuries they played a distinguished part in the history of the Eastern Empire.

The important role played in the history of Byzantium by the Armenians has been generally unrecognized.

Council of Theodosiopolis (593)
After the conclusion of long Byzantine-Persian War (572-591), direct Byzantine rule was extended to all western regions of Armenia. In order to strengthen political control over newly annexed regions, emperor Maurice (582-602) decided to support pro-Chalcedonian fraction of the local Armenian Church. In 593, regional council of western Armenian bishops was convened in Theodosiopolis, and proclaimed full allegiance to the Chalcedonian Definition. The council also elected John (Yovhannes, or Hovhannes) of Bagaran as new Catholicos of Chalcedonian Armenians.

Religion
Armenia is often considered the first country in the world to have adopted Christianity as the official religion. Located at the crossroads between the Greek and Syriac churches, the Armenian Church was influenced by them. The Church of Armenia distances itself from the Imperial Church from the Council of Chalcedon in 451.

The peculiarities of the Armenian Church
The official Christianization of Armenia is attributed to the Bishop of Cappadocia, Gregory the Illuminator at the iv th century. The latter converted King Tiridates as well as the entire royal court and the Armenian nobility After this conversion, Gregory was charged with building the Church of Armenia and organizing his clergy. In the iv th century the Armenian church has several features that make the already different from the imperial Byzantine Church. First of all, the Armenian high clergy is made up of about 12 bishops who are under the direction of a Catholicos, the equivalent of the patriarch. The Catholicos was inspired by the Persian pontiff and was to receive the title at Caesarea in Cappadocia. The king and the head of the Church worked hand in hand. But given the feudal structure of the country, that the Catholicos was working closely with the king caused administrative problems. Then, the pontiffs were very often at the beginning of Armenian ecclesiastical history, people who followed the line of Gregory the Illuminator. However, when there was a civil conflict, it was clerics who were in the line of the Greek bishop Aghbianos or a Syrian bishop who would occupy the post of Catholicos. To simplify, the catholicosGreeks were closer to the Byzantine Church and were more zealots while their Syrian counterparts were less intrusive in the affairs of state and less intense in their beliefs. The very fact that there were clerics of Greek or Syriac inspiration can be explained by the training of priests who were trained in one or the other language depending on the region. In addition, translators were trained to comment on the Eucharist in Armenian before the faithful so that they would understand. Besides, nepotism was almost institutional in this Church at its beginnings. For a few generations, the Catholicos and probably the bishops also passed their title to the next generation. Finally, the v th century saw the birth of the Armenian alphabet that enables the translation of the liturgy and Christian and Christianity has been able to penetrate the popular class. The Armenian Church continued to evolve over time, but it was in the context of conflict with the Byzantine Church that it was transformed.

Conflicts with the Imperial Church
The break between the Armenian and imperial churches originates discussions related to the nature of Christ in the early centuries of Christianity. It must first be understood that the first three councils on the nature of Jesus Christ, those of Nicea, Constantinople and Ephesus, were never a source of controversy in the Church of Armenia and that the Pre-existing conflicts between the two Churches were of an administrative nature. These conflicts were not of the same gravity as the Council of 451. It is, in fact, the Council of Chalcedony which is at the origin of the birth of an autocephalous Armenian Church. When the council took place, the Armenians faced a serious crisis that threatened Christianity in the Sassanid part of their kingdom. Indeed, the king of Persia had ordered the conversion of the Armenians to Mazdéisme. Busy in protecting its religion from the Sassanid threat, Armenia had not sent any representative to the Council of Chalcedon and was not made aware of its conclusions until after the conflict with the Persians. As soon as the Church learned of the content of the council, she immediately rejected it, declaring it Nestorian and thus heretical. Armenians were later labeled as monophysites by the Western Churchand the Eastern Church but the fact is that they were not monophysites but rather adherent to the doctrine of Saint Cyril of Alexandria. This means that they rejected the confusion of the divine and human natures of Christ preached by Eutychès, but that they reject the idea according to which the two natures are united as wanted by the council of Chalcedon. On several occasions, during the following centuries, the Byzantines tried to reconcile their Church with that of the Armenians by various means. First, the Emperor Maurice at the end of the vi th century, has set up a Catholicos rival to try to discredit the Catholicosofficial. The result of this attempt was to create a short schism in the Church of Armenia. Mauritius' successors will also try other approaches, but all of their attempts at compromise have been unsuccessful. During the revival period of royal power in Armenia, negotiations take place between the Byzantines and the Bagratuni kings unsuccessful. Finally, the last attempt at reconciliation takes place at the xii th century Cilician Armenia during the reign of Manuel I Comnenus and is another failure. While it is true that the two Churches were divided during most of the Byzantine period of Armenia, the two Churches also have important points in common. The Armenian liturgy is the liturgy of Saint Basil, a Greek bishop, and the Armenian clergy is equally divided between the black clergy and the white clergy (respectively married and single).

Armenian arts, literature and architecture
The Art of Byzantine Armenia can be subdivided into two main periods: iv e in the first half of the viii th century and the second half of ix th century xi th century. These two periods correspond respectively to the first Byzantine period and the rebirth of royal power under the Bagratides (and the return to the Byzantine Empire).

Arts and architecture of the first Byzantine period (305-750)
In art during this first period, we see many sculptures on the cornices of buildings and sometimes biblical scenes or portraits of patrons inside the buildings. However, it should be understood that the interior decoration is only done in Armenian capitals. Armenian art has in particular that it is not only biblical characters who are represented but also historical characters and laymen 36. During this same period, we can see in illuminations, frescoes and mosaics.In addition, even if Byzantium dominated Armenia during this period, Armenian art has Persian influences as to the manner of representing the clothing and posture of the characters.

In architecture, the churches were built in the shape of a cross and surmounted by domes. These same domes were sometimes supported by horns.

Arts and architecture of the royal renaissance period and second Byzantine period (862-1021)
Although there were internal and external changes during these 7 centuries, there were also several elements of continuity especially in architecture. If architecture, buildings retain substantially the same form they had at the vii th century architectural elements Muslims are part of the sculptural decoration. Indeed, the building stones used are of several colors, the interlacing make their appearance in the decoration and we also see the replacement of the tubes by muqarnas.

In painting, the Armenians mainly use the Byzantine style for their illuminations, their paintings but we also see the influence of Islam in the decorative art of the Gospels. Indeed, King Gagik of Kars had a copy of the Gospels with an image representative with his family in Arab held on the East mats

Armenian literature
In literature, during the first period, texts of Greek philosophy were translated and texts relating to historical facts were written or modified to justify political positions. During the second period, the books of stories multiply. For example, one sees a history book written by Shapuh Bagratid which compiles the history of the deluge to 923. It was not the only one to have been published because even the Arçrouni published their version. We also see history books on other peoples being written at the same period, in particular a History on the Caucasian Albanians. Finally, books of tales and stories are compiled and a national epic titled David Sasun reads.

Commerce

Trade before the Arab invasions
From Late Antiquity, Armenia played a crucial role in trade between the West and the East. During the period when Armenia was between the Byzantine Empire and the Sassanian Persia, Byzantium sold products to the whole world from the Eastern trade routes. The Empire bought silk, ivory, precious stones, spices, pearls, flavored products, gold and other products in the East. In addition, by these same trade routes, Byzantium sold glass products,wine, purple clothing and many other products. These trade routes were not only important for Byzantium, which obtained the silks from China and for Persia, which presumably controlled all eastern trade,but also for Armenia. Indeed, trade between the West and the East benefited the Caucasian state enormously, since many cities were built during this period. In addition, in the commercial treaty between Justinian and Choroes I, king of Persia, there was a clause which preserved the border trade posts of Armenia, which allowed him to remain one of the key pieces of international trade. For commercial transactions, the Armenians, having no proper currency, used Byzantine or Arab coins.

From the reconquest to the battle of Mantzikert
Armenia ceased to benefit fully from foreign trade after the invasion of the Seljuk Turks. But the decline began under the Byzantine reconquest. When the Byzantines were reinstated Armenia in its territory, the landed nobility was moved in Cilicia or in Asia Minor and the imperial administration replaced them. The armed forces of the Bagratids were replaced by the Byzantine soldiers for the defense of the territory. Under Constantin Monomaque and Constantin Doukas, the soldiers' pay was cut, a large part of the forces were demobilized. This strategy aimed to improve the state of the finances of the Empire. The Seljuk's first attacks, therefore, encountered only minimal resistance, which enabled them to march easily to Constantinople.

Armenians in Byzantium

The Imperial Armenians
The Armenians were not exclusively concentrated in the provinces of Armenia I to IV and later in the themes which had been created from the territories of Armenia. Some Armenians lived in Constantinople and others were even colonized the lands far from home as the Balkans and southern Italy in the viii th century. In addition to colonizing certain regions of the Empire, the Armenians, especially the Chalcedonian confessional, held important positions in the imperial army. The Armenian military were Hellenized and played a major role in the x th century in the reconquest of Armenia by the Byzantine. In addition, some Byzantine emperors were Armenian or of Armenian descent, for example Leon V and Jean I er Tzimiskès. It is estimated that the same xi th century, about 10 to 15% of the nobility was of Armenian origin although the nobility was not very close to the Comneno. Finally, late in the xi th century, the Armenian nobles participated in the creation of the Cilician Armenia, an independent state from the Byzantine Empire.

Armenians living in the kingdom of Armenia
Even though the Armenians obviously formed a large ethnic group within the Empire, that does not mean that they were all well regarded. Indeed, Greek Byzantine literature often depicts them as deceitful and prone to betrayal. As for the Armenians who lived in Armenia, the reconquest of their lands by the Byzantines was seen as a betrayal. An example of this is in a chronicle of Matthew of Edessa where he speaks of a betrayal on the part of the Armenian nobles of Byzantium. According to him, due to the acts of the nobility, the king of Armenia would never return to rule his kingdom. During this period, non-Chalcedonian Armenianssee the Greeks as evil beings who seek to destroy their faith and their kingdom. In the aftermath of the Battle of Mantzikert, the Armenians of Cilicia never accepted the Council of Chalcedon and some Armenian nobles turned their backs on the Empire. Those who did not live in Cilician Armenia slowly began to turn against the Emperor. The soldiers were no longer reliable, urban Armenian communities isolated themselves Byzantine fear of seeing their corrupt faith and Armenians Balkans or Troas rebelled alongside the enemies of the Empire.

Urban heat island Urban areas usually experience the urban heat island (UHI) effect, that is, they are significantly warmer than surrounding...